1. Field of the Invention
The subject invention generally pertains to refrigerant systems and more specifically to a refrigerant circuit that offers a reheat mode of operation.
2. Description of Related Art
Conventional refrigeration systems comprising a compressor, a condenser, an expansion valve and an evaporator can be used to meet the sensible and latent cooling demands of a room or area in a building when the room temperature is appreciably above a target temperature. In some circumstances, however, high humidity can leave a room feeling uncomfortable even though the room temperature might be at or even below the target temperature. Although further cooling of the room can reduce the humidity, the additional cooling can make the air in the room feel cold and dank.
To avoid this problem, many refrigerant systems include a reheat mode where a heater downstream of the evaporator raises the temperature of the supply air after the evaporator cools the air to reduce the humidity. Such systems can effectively address the latent cooling or dehumidifying demand without subcooling the room. Although the reheat mode can be provided by electric heat or combustion, the system can be less expensive to operate if the reheat is provided by the refrigerant circuit itself. In some cases, for instance, the compressor discharges relatively hot refrigerant gas into an additional heat exchanger that reheats the air that was previously cooled by the evaporator.
Using an additional heat exchanger in such a manner, however, can create a problem regarding the system's refrigerant charge. Air conditioning systems typically require less refrigerant during a reheat mode than during a cooling-only mode. Unless the system has some means for adjusting its refrigerant charge, the system might have an excessive amount of refrigerant during the reheat mode or an insufficient supply during the cooling mode. Thus, the system's efficiency might suffer in the cooling and/or reheat mode.
Previous systems addressing reheat and charge control include those shown in U.S. Pat. No. 6,122,923 to Sullivan; U.S. Pat. No. 6,170,271 to Sullivan; U.S. Pat. No. 6,381,970 to Eber et al.; and, U.S. Pat. No. 6,612,119 to Eber et al.; all of which are commonly assigned to the assignee of the present invention and all of which are hereby incorporated by reference. Although some systems include a liquid receiver for storing excess refrigerant during the reheat mode, such systems can be expensive due to the cost of the added receiver and associated control valves. Consequently, a need exists for a simpler, more cost effective refrigerant reheat system.